The invention relates to a process for controlling an automated motor vehicle drive train which has an engine and a transmission, with the step of at least once detecting at least one wear parameter of the transmission during its running performance, the wear parameter representing the wear or fatigue of at least one component of the transmission.
The present invention relates, furthermore, to an automated drive train for a motor vehicle with an engine and with a transmission, with means for detecting at least one wear parameter of the transmission and with means for controlling the drive train.
A process of this type and a drive train of this type are known from WO 01/61653 A1. This publication is concerned with a process for determining the remaining operating duration of a product. In this case, values of specific operating variables are detected. The value range of the individual operating variables is subdivided into classes, and the operating durations are detected as a function of the class within which the detected value falls. An assignment of weighting factors may also take place here, in order to determine a weighted cumulative operating duration for a product.
The product, of which the operating duration up to technical failure is detected, may be, for example, an engine, a transmission or a control apparatus of a motor vehicle.
This process for determining the remaining operating duration is intended to make possible a particularly reliable preventive maintenance/repair shortly before the end of the technical running performance is reached.
The term “running performance” is understood in the present context as being a generic term for various terms which may be connected with the stress of a motor vehicle, such as, for example, operating duration, running distance, running time, etc.
In motor vehicles, an essential quality criterion is that the motor vehicle should as far as possible not break down or as far as possible rarely break down within a predetermined average running performance. A critical criterion for this is reliability, that is to say the probability that a product will not break down during a defined running performance under given functional and ambient conditions (cf. “Fahrzeuggetriebe—Grundlagen, Auswahl, Auslegung und Konstruktion” [“Vehicle transmission—principles, selection, design and construction”] by G. Lechner and H. Naunheimer, Springer-Verlag, page 395).
One of the critical criteria for reliability is what is known as the failure rateλ(t) as a measure of the risk of failure of a part when it has already survived up to the distance point (d) or time point (t).
The failure behavior of a product is often exhibited in the form of what is known as a “bathtub curve”. This is formed by three regions. The first region refers to early failures which occur essentially due to assembly or manufacturing errors. A middle region with a relatively low failure rate is the region of random failures caused, for example, by operating faults, dirt or the like.
The third region, in which the failure rate rises sharply with an increase in running performance, is the region of wear or fatigue failures.
The second region can be influenced to only relatively little extent. The first region can be influenced positively by strict manufacturing and quality assurance. In the present context, however, the third region is of particular importance.
This is because a suitable running performance calculation can ensure, in the design of the transmission, that, taking into account all possible circumstances, operation which is as damage-free as possible is achieved beyond the required average running performance expectation.
The emphasis in this case is on freedom from damage or maximum reliability over a defined running performance, for example zero failures within the first 150 000 km.
Since the transmission as a whole fails even in the event of the failure of one part of the transmission (for example, the break of a gearwheel), the individual components of the transmission are in each case to be designed as a function of the load to be expected, such that they all fulfill the average running performance expectation.
The different utilization behavior of consumers is of highly critical importance in this running performance calculation. Thus, as is known, there are vehicle drivers who drive extremely defensively and in this case almost never fully exhaust the performance capacity of their vehicle. On the other hand, there are drivers who constantly demand the available performance from their vehicle. However, performance-preoccupied drivers make up, overall, only a relatively small fraction of users. Nevertheless, as a rule, a transmission is designed such that it possesses a high running performance expectation even for performance-preoccupied drivers.
A simplified illustration of this is assumed below, whereby a transmission possesses an average running performance expectation of 100 000 km, that is to say, on average, does not fail before reaching this driving performance with the vehicle in which the transmission is installed. It will be appreciated, however, that, in practice, the average running performance expectation may even amount, for example, to 150 000 or 200 000 km.
It is apparent from what was said above that, where performance-preoccupied drivers are concerned, the average running performance expectation is about 100 000 km. As regards defensive drivers, however, the transmission will have an average running performance expectation which is markedly higher and may lie, for example, in the region of 300 000 or 400 000 km.
The result of this is that, in the case of defensive drivers, a vehicle which possesses, overall, as a system a running performance of, for example, 100 000 kilometers and fails on account of other components is scrapped, even though the transmission would still be “good” for a further running performance of 200 000 or 100 000 km.
Under these circumstances, designing the transmission in such a way that even performance-preoccupied drivers have a reasonable average running performance expectation leads to the individual transmission parts having a stronger or a larger dimensioning. This contributes to a higher weight of the transmission. In other words, the result of this necessary transmission design is that a large proportion of users (defensive drivers) “drag around” with them an unnecessarily high weight above the average running performance of the vehicle. This leads, in the case of these drivers, to increased fuel consumption and therefore also to higher emissions (in internal combustion engines), etc.
To monitor the functioning of a motor vehicle transmission, it is known from DE 197 31 842 A1 to detect the position of a variable-position transmission element and to check by means of an assessment criterion whether the variable-position transmission element is in a predetermined target position. As a result, a malfunction due to tolerances can be avoided and the running performance can be prolonged.
It is known from the initially mentioned WO 01/61653 A1 to determine the remaining operating duration by means of a running performance estimation, in order to make possible preventively a maintenance/repair before the end of the technical operating duration, that is to say before a failure, is reached.
In general, it is also known to monitor specific parameters, such as, for example, the running time of a vehicle and its load, in order to allow a user-dependent and time-dependent early damage detection (DE 101 61 998 A1).
Thus, for example, it is known to carry out the maintenance intervals of vehicles variably as a function of the load on individual parameters of a vehicle, instead of fixed maintenance intervals of, for example, ten or fifteen thousand kilometers.